<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div class="father">
    父
    <div>
      子
      <div>孙</div>
    </div>
    <div>
      子2
      <!-- <div>孙2</div> -->
    </div>
    <div>
      子3
      <div>孙3</div>
    </div>
  </div>
</body>
<style>
  .father{
    background-color: aquamarine;
    width: 500px;
    height: 500px;
  }
  .father div:nth-child(1) div{
    background-color: blueviolet;
    width: 400px;
    height: 400px;
  }
  .father div:nth-child(2){
    background-color: rgb(31, 163, 119);
    width: 400px;
    height: 400px;
  }
  .father div:nth-child(3){
    background-color: rgb(45, 20, 78);
    width: 400px;
    height: 400px;
  }
</style>
</html>